1. Field of the Invention
The present invention relates to electronic endoscope that observes an observed portion, such as a body cavity. In particular, it relates to a brightness adjustment process using a rotary shutter
2. Description of the Related Art
In an endoscope with a brightness adjustment function, an amount of illuminating-light radiated on an observed object is adjusted by using a stop, or an electronic shutter function is adjusted. In an electronic endoscope with a video-scope, a luminance of the object image is detected on the basis of image-pixel signals, which are successively read from a CCD provided in the video-scope. Then, an opening-degree of a stop or an electronic shutter speed (charge-accumulation interval) is adjusted such that the displayed object image is maintained at a proper brightness
In the case of an electronic endoscope with a rotary shutter mechanism, two rotary shutters opposite each other are arranged between a lamp and a light-guide or fiber-optic bundle; and are driven so as to rotate at a constant speed in synchronization with each other. Each rotary shutter has a light-transmitting portion that transmits illuminating-light, and a shield portion blocking the illuminating light. To adjust the brightness of the observed image, an overlapped area of the two light-transmitting portions, which allows illuminating-light to progress toward the incident surface of the light-guide, is changed by shifting a relative position of one rotary shutter relative to that of the other rotary shutter before performing the brightness adjustment process.